User's Manual

Design
P/N 81-CO2MAN-001 3-19 September 2013
3-5.3 Calculations for Deep-Seated Fires
Deep-seated fires involve a combination of surface fire and burning within a mass of material.
The surface burning is quickly suppressed when a sufficient quantity of carbon dioxide is rapidly
discharged into the protected enclosure. However, to extinguish the burning within the mass
of material, a sufficiently high concentration must be maintained for an appropriate time period
to allow any smoldering to be suppressed and to allow the material to cool to a temperature
at which it will not reignite when the carbon dioxide dissipates.
Applications that contain materials that produce surface fires may also contain varying
amounts of material that will produce deep-seated fires. Each application must be carefully
analyzed to determine the most appropriate suppression approach. The decision to design the
suppression system for a surface fire or for deep-seated combustion is usually based upon
considerations such as speed of detection versus time to extinguish, mass of materials
involved, thermal insulating factors, manual firefighting capabilities and the economic
importance of the equipment or materials involved. Often the decision will be made after
consultation with the authority having jurisdiction, the owner, and the manufacturer supplying
the equipment or material.
To ensure extinguishment of a smoldering fire, the design concentration must be maintained
for at least 20 minutes. A longer duration of protection may be necessary, depending on the
cooling rate of the smoldering fuel. To accomplish this, a separate extended discharge system
may be necessary to compensate for uncloseable openings and forced ventilation that cannot
be shut off or dampered. (See Paragraph 3-9).
3-5.3.1 FLOODING FACTORS
Carbon dioxide concentrations for deep-seated fires cannot be determined with the same
degree of accuracy as those for surface-burning fires. Flooding factors for deep-seated fires
have been determined on the basis of practical testing. The design concentrations shown in
Table 3-3 must be used for the applications cited.
Flooding factors for other deep-seated hazards must be determined by specific testing and
justified to the satisfaction of the authority having jurisdiction before use.
(Equation 12)
or
Where:
= Quantity of agent for design concentration, lb. (kg)
= Enclosure volume,
ft.
3
(m
3
)
= Volume factor from Table 3-3,
ft.
3
/lb. (m
3
/kg)
= Volume factor from Table 3-3, lb./
ft.
3
(kg/m
3
)
W
C
Vf
1
=
W
C
Vf
2
=
W
C
V
f
1
f
2